Spinning units are known in open-end rotor spinning frames wherein the rotor shaft of the spinning rotor, which typically revolves at a high number of revolutions, is supported in the wedge-like bearing area of a support disk bearing arrangement and is fixed in place by means of a mechanical axial bearing arranged at the end of the shaft. Here, the support disk bearing arrangement comprises two pairs of support disks disposed adjacent one another to define the bearing wedge area therebetween, with the axes of the support disks offset such that an axial thrust is exerted on the rotor shaft to constantly urge the rotor shaft against the mechanical axial bearing arranged at its end.
This type of seating of open-end spinning rotors which, for example, is described in German Patent Publication DE-OS 25 14 734, has proven itself in actual use and makes it possible for the spinning rotors to achieve rotational speeds of greater than 100,000 rpm.
However, because of the offset of the support disks, this type of seating of spinning rotors suffers the disadvantage of increased friction occurring between the bearing surfaces of the support disks and the rotor shaft, which over time leads to heating of the bearing surfaces of the support disks. Not only are the bearing surfaces of the support disks considerably stressed by this frictional heating, but additional energy is also required to overcome this friction. Moreover, the mechanical axial bearings are subjected to not inconsiderable wear, even when properly lubricated.
Therefore attempts have already been made in the past to replace these mechanical axial bearings with wear-resistant magnetic bearings. An axial magnetic bearing arrangement is described in DE 195 42 079 A1, wherein one magnetic bearing element is stationarily fixed in a housing of the axial bearing, and another magnetic bearing element or elements are releasably arranged on the rotor shaft of the spinning rotor. Different variations are proposed in this reference regarding the attachment to the rotor shaft of the magnetic bearing elements so as to thereby rotate integrally with the spinning rotor.
Some of these proposals relate to a frictional fitting of the co-rotating magnetic bearing elements on the shaft, while other proposals relate to an interlocking connection of the co-rotating magnetic bearing elements, which can be easily released if required. Although a correct axial fixation of the rotor shaft on the support disk bearing arrangement is possible with these known magnetic bearing elements, and although it is furthermore assured that the spinning rotor can be installed and removed without problems when required, it has been shown that the frictional connection of the magnetic bearing component with the rotor shaft, which is basically advantageous in that it can be easily released when required, is still capable of improvements. The fastening of the co-rotating magnetic bearing elements on the rotor shaft is particularly problematical in connection with such magnetic bearing devices, because the high number of revolutions of the spinning rotor places great demands on the balancing quality of this connection.
An open-end rotor spinning arrangement with a permanent magnet axial bearing has also become known from Austrian Letters Patent 270 459. In this bearing arrangement, ferromagnetic annular shoulders are arranged at the end of the rotor shaft of a spinning rotor, and pole shoes of a permanent magnet, which is pivotably seated in this area, are placed opposite the annular shoulders. The bundling of the magnetic lines of force of the permanent magnet, which becomes possible by means of such an arrangement, leads to a relatively stiff fixation of the rotor shaft in the bearing wedge of the support disk bearing arrangement.
However, this type of magnetic bearing arrangement has the disadvantage that the annular shoulders arranged on the rotor shaft clearly have a larger diameter than the rotor shaft itself. Since the larger diameter annular shoulders make considerably more difficult or even prevent the installation and removal of the spinning rotor, in particular the mounting of its front, this known magnetic bearing arrangement has been unable to gain acceptance in actual use.
Furthermore, a bearing for a spindle of a textile machine, which rotates at a relatively high number of revolutions, is known from German Patent Publication DE 30 47 606 A1. Here, the spindle is supported in the radial direction by means of a three-point bearing arrangement similar to a support disk bearing, and the spindle is secured in the axial direction by means of a magnetic bearing. At its end, the spindle has a bearing area with a reduced diameter and with two ferromagnetic annular shoulders. A bushing made of a non-magnetic material is fixed in place on the bearing housing, and a ring-shaped permanent magnet element, which is enclosed in lateral pole disks, has been embedded in it. In the installed state of the spindle, the ferromagnetic annular shoulders of the spindle shaft are located opposite the pole disks of the permanent magnet element fixed in the static bearing element. Although this known embodiment permits a relatively problem-free installation and removal of the spindle in the axial direction, this arrangement has not been able to gain acceptance in actual use because of its lack of axial bearing rigidity.
Moreover, other bearings for spinning rotors are known from German Patent Publication DE 197 29 191 A1, or the later published German Patent Publication DE 199 10 279.1, wherein the shaft of the rotor is supported without axial thrust in the bearing wedge of a support disk bearing and is axially fixed in place by means of an axial bearing. In this case the axial bearing has a stationary magnetic bearing component, which can be fixed in place on the bearing housing, and a rotatably arranged magnetic bearing component constituted by ferromagnetic annular shoulders in the area of the end of the rotor shaft. Here, the annular shoulders are constituted by recesses in the rotor shaft, which are subsequently filled with a non-magnetic filler material. In this manner, it is intended to avoid the danger that a coating on the peripheral running surfaces of the support disks might be damaged by sharp-edges of the annular shoulders during the installation or removal of the spinning rotor.
In accordance with German Patent Publication DE 197 29 191 A1, plastic is provided as the filler material but without completely satisfactory results because, at the high speed of rotation of the spinning rotor, the plastic material has a tendency to "flow" after extended periods of operation, which results in an unacceptable imbalance of the spinning rotor.
Although these difficulties could be prevented by filling the recesses with a non-magnetic metallic material as described in German Patent Publication DE 199 10 279.1, this filling of these recesses, for example with copper, can lead to an accumulation of material outside of the bearing area of the rotor shaft, which had a negative effect on the natural oscillation behavior of the spinning rotor, in particular at numbers of revolutions clearly above 100,000 min.sup.-1.